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• Surface Water Ou flows <br />Surface water outflows in the South Platte River water budget (445 kaf/yr) are greater than those <br />from the studies reviewed (300 kaf/yr to 393 kaf/yr) with the differences likely due to variable <br />study periods. The surface water outflows in the North Platte River and Laramie River water <br />budgets are similar to those from the studies reviewed. <br />• Ground Water Ou~ows <br />Ground water outflows from the South Platte River basin were pulled directly from the Bittinger <br />et al., Hurr et al., and CWRRI CR190 studies. <br />Changes in Storage <br />Some of the studies reviewed (Bittinger et al. and Hurr et al.) estimated losses in ground water <br />storage from the South Platte River main stem alluvial aquifer. These changes in ground water <br />storage should be revisited after the surface water and ground water models are developed for <br />the SPDSS effort, which will address the complex ground water/surface water interactions and <br />changes in storage within the SPDSS study area. <br />Comments and Concerns <br />Development of the initial water budgets have provided preliminary estimates for the various <br />water budget components that will be revised with more refined estimates developed in future <br />tasks included in the SPDSS modeling effort. <br />Water budget components that have been improved over previous water use investigations <br />include: <br />1) Consumptive uses caused by human activities <br />- The agricultural consumptive uses over the entire basins were not adequately addressed in <br />the studies reviewed. Crop CU was estimated for the initial water budgets by using <br />Blaney-Criddle crop demands for the total irrigated acreage in the basins. These estimates <br />will be improved as the GIS Land Classification sub-task better identifies the amount of <br />irrigated lands in the basin and their supply source, Blaney-Criddle locally calibrated crop <br />coefficients are developed, and the historical crop consumptive use analysis is completed <br />in Task 59 and Task 74. <br />- Municipal, commercial, and industrial CU was estimated for the current population in the <br />entire basin using estimates ofper-capita water demands developed for SWSI. Other <br />estimates of M&I uses found in the literature were outdated. <br />- Reservoir and stock pond evaporation and livestock CU were included for the entire basin. <br />Estimates of these terms were incomplete in previous studies reviewed including water <br />budget components. <br />We believe the initial SPDSS water budget estimates provide a better representation of the <br />overall water balance in the SPDSS study area than previous estimates. The SPDSS inflows and <br />outflows are based on more detailed analyses and represent a longer period of record than <br />previous modeling efforts. Based on our review, the water budget components with the greatest <br />uncertainty are the amount of native vegetation CU and the changes in ground water storage. <br />Task83 final.doc 10 of 15 Apri17, 2005 <br />